Detector array utilizing air gaps as a reflector between array elements

ABSTRACT

A detector array including a plurality of scintillators for use in association with an imaging device. The detector array is provided for accurate determination of the location of the impingement of radiation upon an individual scintillator detector. An air gap is disposed between the scintillator elements, thereby increasing the packing fraction and overall sensitivity of the array. The amount of light transmitted down the scintillator element and the amount of light transmitted to adjacent elements is modified to optimize the identification of each element in a position profile map by adjusting the surface finish of the detector elements.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] 1. Field of Invention

[0004] This invention pertains to a method for fabricating a detectorarray for use in imaging applications such as X-ray imaging,fluoroscopy, positron emission tomography (PET), single photon emissioncomputed tomography (SPECT), computed tomography (CT), gamma camera anddigital mammography systems. More particularly, the present inventionprovides a simple and highly effective detector array design and itsfabrication with high packing fraction resulting in greater sensitivitywhile still maintaining spatial resolution.

[0005] 2. Description of the Related Art

[0006] In the field of imaging, it is well known that imaging devicesincorporate a plurality of scintillator arrays for detectingradioactivity from various sources. It is also common practice, whenconstructing scintillator arrays composed of discrete scintillatorelements, to pack the scintillator elements together with a reflectivemedium interposed between the individual elements creating photonboundaries. Conventionally the reflective medium serves to collimate thescintillation light along the crystal element into a light guide toaccurately assess the location at which the radiation impinges upon thedetector elements. The reflective medium further serves to increase thelight collection efficiency from each scintillator element as well as tominimize the cross-talk, or light transfer (transmission of light), fromone scintillator element to an adjacent element. Reflective mediumsinclude reflective powders, film, paint, adhesives doped with reflectivepowders or a combination of materials.

[0007] Conventionally, scintillator arrays have been formed frompolished or rough crystals that are either: hand-wrapped in reflectivePTFE tape and bundled together; glued together using a white pigmentsuch as BaSO₄ or TiO₂ mixed with an epoxy or RTV; or glued to a glasslight guide with defined spacing and afterwards filled with reflectivematerial as discussed above.

[0008] Another approach utilizes individual reflector pieces that arebonded to the sides of the scintillator element with the aid of abonding agent. This process requires iterations of bonding and cuttinguntil a desired array size is formed.

[0009] Other devices have been produced to form an array of scintillatorelements. Typical of the art are those devices disclosed in thefollowing U.S. Patents: Pat. No. Inventor(s) Issue Date 3,936,645 A. H.Iverson Feb. 3, 1976 4,749,863 M. E. Casey Jun. 7, 1988 4,914,301 Y.Akai Apr. 3, 1990 4,982,096 H. Fujii et al. Jan. 1, 1991 5,059,800 M. K.Cueman et al. Oct. 22, 1991 6,292,529 S. Marcovici et al. Sep. 18, 2001

[0010] Of these patents, the '645 patent issued to Iverson discloses aradiation sensitive structure having an array of cells. The cells areformed by cutting narrow slots in a sheet of luminescent material. Theslots are filled with a material opaque to either light or radiation orboth. The '800 patent issued to Cueman et al., discloses a similarscintillator array wherein wider slots are formed on the bottom of thearray.

[0011] Most of the aforementioned methods require a separate light guideattached to the bottom of the detector array to channel and direct thelight in a definitive pattern on to a receiver or set of receivers suchas photomultiplier tubes or diodes. This light guide usually containscuts in varying depths to alter the light pattern on the receivers. Inaddition the cuts are filled with reflective material as discussed in'863 patent issued to Casey.

BRIEF SUMMARY OF THE INVENTION

[0012] The present invention is a detector array for use in imagingapplications such as X-ray imaging, fluoroscopy, positron emissiontomography (PET), single photon emission computed tomography (SPECT),computed tomography (CT), gamma camera and digital mammography systems.The detector array includes a plurality of scintillators for use inassociation with an imaging device. The array is fabricated such thatthe location of the impingement of radiation upon an individualscintillator detector, or crystal element, is accurately determinable.This design allows an efficient, consistent, accurate, andcost-effective process for creating an array with high packing fraction,high light output, high sensitivity and high uniformity.

[0013] The detector array of the present invention provides an air gapbetween the individual scintillator elements, thereby eliminating theneed for reflective material. The crystal elements are closely packedtogether and held by friction. The close packing minimizes the spacingbetween the crystal elements and therefore maximizes the packingfraction or array sensitivity. In addition, the detector array of thepresent invention simplifies the light guide by eliminating the cuts andallowing the use of an uncut light guide. The required thickness of thelight guide is significantly reduced relative to light guides used inassociation with prior art detector arrays, thereby effectively reducingthe amount of light absorption in the light guide.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0014] The above-mentioned features of the invention will become moreclearly understood from the following detailed description of theinvention read together with the drawings in which:

[0015]FIG. 1 is a perspective illustration of the detector array of thepresent invention;

[0016]FIG. 2 is a side elevation view of the array, in section, takenalong lines 2-2 of FIG. 1;

[0017]FIG. 3 is a perspective illustration of the detector array of thepresent invention in use in association with a block detector;

[0018]FIG. 4 is a perspective illustration of the detector array of thepresent invention in use in association with a panel detector;

[0019]FIG. 5 is a position profile map acquired from a radioactive floodirradiating the array embodied into a block detector;

[0020]FIG. 6 is an energy resolution map acquired from a radioactiveflood irradiating the array embodied into a block detector.

DETAILED DESCRIPTION OF THE INVENTION

[0021] A detector array and method of fabrication thereof for use inimaging applications such as X-ray imaging, fluoroscopy, positronemission tomography (PET), single photon emission computed tomography(SPECT), computed tomography (CT), gamma camera and digital mammographysystems is provided. The detector array is illustrated at 10 in thefigures. The detector array, or array 10, includes a plurality ofscintillators 12 for use in association with an imaging device (notillustrated). The array 10 is fabricated such that location of theimpingement of radiation upon an individual scintillator detector 12 isaccurately determinable. The present invention provides for the creationof a highly packed, high light output, high sensitivity, uniform,scintillator array 10 in an efficient, consistent, accurate andcost-effective manner. Air gaps 14 are formed between the scintillatorelements.

[0022] As best illustrated in FIG. 1, the array 10 defines an M×N arrayof scintillator elements 12. In the illustrated embodiment, the array 10defines a 12×12 matrix of scintillator elements 12. However, it will beunderstood that “M” and “N” are independently selectable, with “M” beingless than, equal to, or greater than “N”. It will also be understoodthat, while the array 10 is illustrated as defining a squarescintillator array, it will be understood that the array 10 of thepresent invention is not limited to this configuration. The array 10 canbe of one or a combination of more than one geometric configuration suchas diamond, triangular, rectangular, hexagonal, and octagonal.

[0023]FIG. 2 illustrates a cross-sectional view of the array 10 inFIG. 1. The width of the air gaps 14 is exaggerated for clarity. The airgaps 14 in the present invention are dependent upon the surface finishof the detector elements 12. To this extent, in the preferredembodiment, the scintillator elements 12 are optimized in order tomaximize the light collection efficiency of the array 10. Optimizationof the scintillator elements 12 in some applications entails polishingthe surfaces to achieve a selected finish. The scintillator elements 12are tightly packed and held together either in a friction fit or bybonding the scintillator elements 12 to a selected surface.

[0024] To this extent, a mechanism 16 for maintaining the relativepositions of the individual scintillator elements 12 with respect toeach other is provided. In the illustrated embodiment of FIGS. 1-3, themechanism 16 is a retainer disposed about the outermost scintillatorelements 12 to maintain the relative positions of the individualscintillator elements 12. The retainer 16 is fabricated fromconventional materials such as shrink wrap, rubberized bands, tape or acombination of like materials may be used to enclose or hold the arraytogether in a tight, uniform fashion. Although illustrated as spanningthe entire height of the array 10, the retainer 16 may in someapplications include one or more retainers 16 which span only a portionof the height of the array 10.

[0025] In the embodiment illustrated in FIG. 4, the mechanism 16 is abonding agent applied between one end of each scintillator element 12and a light guide 20. As discussed below, the light guide 20 is notrequired in all applications. Accordingly, although not illustrated, inthose applications that scintillator elements 12 are bonded to thephotodetectors 18.

[0026] The air gaps 14, in conjunction with the surface finish of thescintillator elements 12, define the light collection efficiency of thescintillator elements 12 as well as the amount of light sharing thatoccurs between the elements 12. The significant change in the index ofrefraction (IOF) from a scintillator element 12 and air 14 increases theangle of total refraction. Based on the ratio IOF(scintillator)/IOF(air)and the surface finish of the scintillator element 12 the amount ofscintillation light photons is tuned such that a controlled amount ofphotons are collimated down through a scintillator element 12 and acontrolled amount are transmitted to neighboring elements 12. Theoptimal ratio is customized for each scintillator element 12 within thearray 10 such that each element 12 in the array 10 is clearlyidentified. The ratio may be spatially variant.

[0027] Illustrated in FIG. 3 is a three-dimensional view of the array 10composed of scintillator elements 12. The array of scintillator elements10 is coupled to at least one photodetector 18 selected from, but notlimited to, photomultiplier tubes, position sensitive photomultipliertubes, avalanche photodiodes, pin diodes, CCDs, and other solid statedetectors.

[0028] A light guide 20 is selectively placed between the array 10 andthe receiving photodetectors 18. The light guide 20 defines a selectedconfiguration, such as being segmented or continuous. It will beunderstood that the light guide 20 is optional and, when employed, isoptimized depending on the choice of scintillator elements 12 andphotodetectors 18.

[0029] In this arrangement, the scintillators 12 disposed within thearray 10 serve to detect an incident photon and thereafter produce alight signal corresponding to the amount of energy deposited from theinitial interaction between the photon and the scintillator element 12.The array 10 serves to reflect and channel the light down thescintillator element 12 to the coupled light guide 20 and to thephotodetector 18. The signal generated by the photodetector 18 is thenpost-processed and utilized in accordance with the purpose of theimaging device.

[0030] Illustrated in FIG. 4 is a plurality of arrays 10 disposed abovea continuous light guide 20. As discussed previously, the relativepositions of the individual scintillator elements 12 are maintained viaa mechanism 18 which is a bonding agent applied between the scintillatorelements 12 and the continuous light guide 20. The continuous lightguide 20 is disposed above an array of photodetectors 18, such as in apanel detector.

[0031]FIG. 5 illustrates a position profile map acquired from floodirradiating a detector array 10 of the present invention. FIG. 6illustrates the energy spectra relative to each of the scintillatorelements 12 in the detector array 10 used to acquire the energyresolution map of FIG. 5.

[0032] From the above description, it will be recognized by thoseskilled in the art that a detector array having high packing fractionand high sensitivity has been disclosed. The detector array ismanufactured using a consistent, cost-effective method. The detectorarray includes a plurality of scintillators for use in imagingapplications such as X-ray imaging, fluoroscopy, positron emissiontomography (PET), computed tomography (CT), gamma camera and digitalmammography systems. The array has an air gap between the scintillatorelements, thereby increasing the packing fraction and eliminating theneed for light partitions or reflective partitions in between theelements. The change in index of refraction and the surface finishallows light to be collimated along the scintillator elements whilecontrolling cross-talk between the discrete scintillator elements. Theair gap will not absorb scintillation photons to a degree such asreflective material. Therefore, the presented design allows the controlof light spread along and between the scintillator elements in thedetector array for optimized positioning while maximizing the amount ofdetectable light photons by the photodetector. Thus, the light output ofthe array as well as the uniformity of light output from eachscintillator element is significantly improved compared to conventionalarrays using reflective materials.

[0033] While the present invention has been illustrated by descriptionof several embodiments and while the illustrative embodiments have beendescribed in considerable detail, it is not the intention of theapplicant to restrict or in any way limit the scope of the appendedclaims to such detail. Additional advantages and modifications willreadily appear to those skilled in the art. The invention in its broaderaspects is therefore not limited to the specific details, representativeapparatus and methods, and illustrative examples shown and described.Accordingly, departures may be made from such details without departingfrom the spirit or scope of the general inventive concept.

Having thus described the aforementioned invention, we claim:
 1. Adetector array comprising: an M×N array of scintillator elements where“M” and “N” are independently selectable, said array of scintillatorelements defining a plurality of outermost scintillator elements; an airgap defined between adjacent said scintillator elements; and a mechanismfor maintaining a relative position of each of said array ofscintillator elements with respect to each of said array of scintillatorelements.
 2. The detector array of claim 1 wherein each of said array ofscintillator elements defines a top surface, a bottom surface, and aplurality of side surfaces, and wherein each of said plurality of sidesurfaces is optimized to define a selected light collection efficiencyand to control light sharing between said array of scintillatorelements.
 3. The detector array of claim 1 further comprising at leastone photodetector, said array of scintillator elements being coupled tosaid at least one photodetector.
 4. The detector array of claim 3wherein said mechanism for maintaining a relative position of each ofsaid array of scintillator elements with respect to each of said arrayof scintillator elements is a bonding agent for bonding each of saidarray of scintillator elements to said at least one photodetector. 5.The detector array of claim 3 wherein said at least one photodetector isselected from the group consisting of at least a photomultiplier tube, aposition sensitive photomultiplier tube, an avalanche photodiode, a pindiode, a CCD, and a solid state detector.
 6. The detector array of claim3 further comprising a light guide disposed between said array ofscintillator elements and said at least one photodetector, saidscintillator elements being coupled to said at least one photodetectorvia said light guide.
 7. The detector array of claim 6 wherein saidmechanism for maintaining a relative position of each of said array ofscintillator elements with respect to each of said array of scintillatorelements is a bonding agent for bonding each of said array ofscintillator elements to said light guide.
 8. The detector array ofclaim 6 wherein said light guide is configured to be continuous over aplurality of said array of scintillator elements and a plurality of saidat least one photodetector.
 9. A detector array comprising: an M×N arrayof scintillator elements where “M” and “N” are independently selectable,said array of scintillator elements defining a plurality of outermostscintillator elements, each of said array of scintillator elementsdefining a top surface, a bottom surface, and a plurality of sidesurfaces, and wherein each of said plurality of side surfaces isoptimized to define a selected light collection efficiency and tocontrol light sharing between said array of scintillator elements; anair gap defined between adjacent said scintillator elements; a mechanismfor maintaining a relative position of each of said array ofscintillator elements with respect to each of said array of scintillatorelements; and at least one photodetector, said array of scintillatorelements being coupled to said at least one photodetector.
 10. Thedetector array of claim 9 wherein said mechanism for maintaining arelative position of each of said array of scintillator elements withrespect to each of said array of scintillator elements is a bondingagent for bonding each of said array of scintillator elements to said atleast one photodetector.
 11. The detector array of claim 9 wherein saidat least one photodetector is selected from the group consisting of atleast a photomultiplier tube, a position sensitive photomultiplier tube,an avalanche photodiode, a pin diode, a CCD, and a solid state detector.12. The detector array of claim 9 further comprising a light guidedisposed between said array of scintillator elements and said at leastone photodetector, said scintillator elements being coupled to said atleast one photodetector via said light guide.
 13. The detector array ofclaim 12 wherein said mechanism for maintaining a relative position ofeach of said array of scintillator elements with respect to each of saidarray of scintillator elements is a bonding agent for bonding each ofsaid array of scintillator elements to said light guide.
 14. Thedetector array of claim 12 wherein said light guide is configured to becontinuous over a plurality of said array of scintillator elements and aplurality of said at least one photodetector.
 15. A detector arraycomprising: an M×N array of scintillator elements where “M” and “N” areindependently selectable, said array of scintillator elements defining aplurality of outermost scintillator elements, each of said array ofscintillator elements defining a top surface, a bottom surface, and aplurality of side surfaces, and wherein each of said plurality of sidesurfaces is optimized to define a selected light collection efficiencyand to control light sharing between said array of scintillatorelements; an air gap defined between adjacent said scintillatorelements; a mechanism for maintaining a relative position of each ofsaid array of scintillator elements with respect to each of said arrayof scintillator elements; at least one photodetector; and a light guidedisposed between said array of scintillator elements and said at leastone photodetector, said scintillator elements being coupled to said atleast one photodetector via said light guide.
 16. The detector array ofclaim 15 wherein said at least one photodetector is selected from thegroup consisting of at least a photomultiplier tube, a positionsensitive photomultiplier tube, an avalanche photodiode, a pin diode, aCCD, and a solid state detector.
 17. The detector array of claim 15wherein said mechanism for maintaining a relative position of each ofsaid array of scintillator elements with respect to each of said arrayof scintillator elements is a bonding agent for bonding each of saidarray of scintillator elements to said light guide.
 18. The detectorarray of claim 15 wherein said light guide is configured to becontinuous over a plurality of said array of scintillator elements and aplurality of said at least one photodetector.